1. Field of the Invention
The present application relates to the use of modified nanoparticles, a process for producing wood based panels using modified nanoparticles and a wood based panel producible in such a process.
2. Description of Related Art
As is known wood based panels consist of lignocellulose or lignocellulose containing materials, such as wood fibres or wood shavings. Lignocellulose comprises cellulose, hemicellulose and lignin as ingredients. Cellulose is a long chain macromolecule consisting of glucose units, hemicellulose is a short chain branched macromolecule of pentoses and lignin is a three-dimensional macromolecule of methoxyphenylpropane units. Cellulose and hemicellulose form the structural substance of the cell wall, while lignin as filling substance in the cell structure causes lignification.
In the course of producing wood based panels and in particular due to the production process of wooden shavings a multitude of volatile organic compounds are produced or released. Volatile organic substances, which easily evaporate or are already present as a gas at lower temperatures, as for example room temperature, belong to the volatile organic compounds also called VOCs.
All the compounds, which are highly volatile or already present in gaseous form at low temperatures belong to the highly volatile organic compounds. The boiling point of the organic compounds belonging to the VOCs is typically in a range between 50 to 260° C. However, the definition of VOCs is country specific and varies accordingly.
In particular when using construction products, such wood based panels in interior spaces the emission of highly volatile organic compounds constitutes a particular health relevant source of impact.
In Germany the health evaluation of emission of volatile organic compounds in interior spaces of buildings is carried out by the Committee for the Health Evaluation of Construction Products (AgBB). According to the criteria established by the Committee volatile organic compounds (VOC) comprise substances in the retention range C6 to C16 and low volatile organic compounds (SVOC) comprise substances in the retention range above C16 to C22. The highly volatile organic compounds (VOC) are thereby considered either as singular substance or in the sum as TVOC (total volatile organic compound).
The VOC emission of construction products is typically investigated in test chambers. The TVOC value of suitable construction products should be according to AgBB criteria after 3 days at 10 mg/m3 or below and after 28 days at 1 mg/m3 or below (AgBB evaluation scheme for VOC for wood construction products, 2010).
Comparable guidelines were established by the Bundesumweltamt according to which a VOC emission of less than 300 μg/m3 is classified as hygienically harmless (Umweltbundesamt 2007, Bundesgesundheitsblatt 7, pages 999-1005).
In the wood processing industry the highly volatile organic aldehydes, such as formaldehyde or hexanal as well as the highly volatile terpenes are of particular importance.
Accordingly, the present application relates to the reduction of aldehydes and terpenes, in particular monoterpenes. Aldehyde, such as hexanal originate thereby either from the natural ingredients in the wood or from an oxidative degradation of natural fats. Terpenes are contained in the natural wood ingredient resin.
In general the volatile organic compounds result either as side products during the production process or they are released slowly during the use of the product to the ambient air. Those processes provide specific problems, which can increase the cost for the whole production process and/or result in odour nuisance when using wood fibre panels.
The volatile organic compounds VOC are either already present in the wood material or are released therefrom during processing or are formed according to the present knowledge by the degradation of non-saturated fatty acids, which again are degradation products of wood. Typical conversion products, which appear during processing, are for instance pentanal or hexanal but also octanal, octenal or 1-heptenal. In particular coniferous wood, which is used primarily for the production of medium-dense fibre panels or OSB-panels, contain large amounts of resins and fats, which cause the formation of volatile organic terpene compounds and aldehydes. VOC and aldehydes, like formaldehyde, can however also arise when using specific glues for the production of wood materials.
VOC-emission is accordingly exclusively based on wood related releases, which can be subdivided in primary emission of highly volatile wood ingredients such as terpenes or chemical degradation products, such as acetic acid, and so called secondary emissions, as for example higher aldehydes, like pentanal or higher carboxylic acids.
The VOC-emission can provide a considerable problem depending on the use of the wood based panels as for instance in form of OSB-panels and depending on the space load. Apart from that the emission of VOCs is a disadvantage for the wood fibre insulating material which is as such ecological in comparison to others, for instance mineral insulating materials.
Due to the mentioned reasons it is thus desired to reduce the release of volatile organic compounds from wood based panels.
Different approaches were chosen therefore in the past. DE 10 2007 050 935 A1 describes a process for producing wooden materials, wherein a gluten containing adhesive, a milk protein containing adhesive, a plant protein containing adhesive or derivatives of these adhesives were added to the wood fibres before pressing. Gluten containing adhesives are hide glue, bone glue, leather glue; milk protein containing adhesives are amongst others casein adhesives and plant protein containing adhesives are amongst others soy adhesives.
In US 2009/0130474 A1 aldehyde scavengers are added to a wood material or binding material. Bisulfites, pyrosulfites, as for example sodium hydrogensulfit, potassium hydrogensulfit, zinc sulfit, magnesium sulfit or aluminium sulfit and dithionites are described here as typical aldehyde scavengers.
According to WO 2010/136106 a zeolite as aldehyde scavenger is added to the mixture of wood fibres and adhesive during the production of wood material products. When using zeolites as aldehyde scavenger few disadvantages however arise. For instance relative high amounts of about 5% to atro wood have to be added.